Structure and Flow in the Margin of the Law Dome Ice Cap. Antarctica (Abstract)

Abstract

The internal structure of the Law Dome ice cap is being investigated by studying ice cores obtained from several sites along the summit-Cape Folger line. Profiles of measured physical properties for four of the ice cores from near the margin of the ice cap are presented. A comparison of the profiles shows a gradual increase and then decrease in crystal size, and the development of strong crystal anisotropy in the upper half of the ice thickness. But in the lower part there is a complex multi-layer crystallographic structure, with an interleaving of ice which has markedly different physical properties. The development of the physical properties in the ice cores is discussed in terms of the deformation in the ice cap in the neighbourhood of the bore holes and the movement of the ice over the rough bedrock. The interdependence of the physical properties and the flow within the ice cap and their effect on other proxy records obtained from the ice cores are also explored.The Law Dome is a small ice cap, about 200 km in diameter, adjoining the main Antarctic ice sheet. It is being studied as a model ice cap, using surface surveys and ice-core drilling. It is large enough to have most of the features of larger ice sheets but small enough to be investigated in considerable detail. The four cores were drilled within 10 km of the coast at Cape Folger and lie approximately along a flow line. Each of the cores covers the Holocene and at least the later part of the Last Glacial Maximum. Two of the cores are within 40 m of bedrock and the remaining two, in thinner ice nearer the coast, are within a few metres of bedrock. Physical properties which were measured include: crystal size, texture and orientation; bubble size, orientation and distribution; and visible stratigraphy. The stratigraphy in the upper layers is related mainly to the occurrence of surface melting during the warmer months of the year. Additional supporting information is available from measurements of the physical properties on shallow cores up-stream of the four bore holes, from radio echo-sounding profiles and from other studies on the ice cores. This data is used in the discussion of the velocity field in the ice cap.